Telephone service carriers, including both mobile cellular and PCS networks, provide a number of different features which may be used by a network subscriber at the subscriber's discretion. A non-exhaustive list of features which may be provided include Call Forwarding, Call Waiting, Calling Number Identification, Automatic Callback, Conference Calling, Message Waiting Notification, Call Encryption, Selective Call Acceptance, Voice Mail, Enhanced Vocoder, and Cost of Call Notification. Activation or deactivation of such features typically involves the completion of a sequence of keystrokes on the keypad to enter the "feature code", also known as a "vertical service code" or "VSC", for selecting or de-selecting the desired feature. The keystrokes may involve the entry of a numeric sequence preceded by the star key (*) and/or followed by the pound key (#), e.g., "*66#", or may involve the selection of a dedicated menu by pressing a "Menu" key followed by a one- or two-digit number, one or more soft keys, or by scrolling the menu screen. Even when a mobile unit has menu capability, the feature code value specific to the home network is commonly a numeric sequence as above, with selection of the "Menu" key being sent as a star key to indicate a feature code. In this case, the feature code value is programmed upon activation of the feature to correspond to a particular menu location, and the actual feature code value is unknown to the user.
While the network subscriber may become thoroughly familiar with the procedure for access feature codes within his or her home network and mobile phone, several obstacles to the optimal usage of such features exist as a result of the lack of standardization within the communications industry. These obstacles may appear because, for example, the feature code for any given feature may be different from one network to another, not all networks provide all features, and there is a large number of different types of telephones, many of which may not support such features, or which have their own pre-determined menu-based sequence for selecting feature codes. While these issues may pose little practical difficulty for wire-based network subscribers, mobile phone users frequently travel between coverage areas of different network service providers and, thus, are likely to experience the loss of, or inability to control, a desired feature. Under current practices, the only way that a mobile user can determine whether his or her feature code matches the corresponding code for the visited network is to try it. If the entered value matches, an acknowledging tone or message will be received at the mobile unit. If the code does not match, a different tone or message will indicate an unsuccessful entry. While little may be done if a mobile user has entered an area covered by a visited network that simply does not offer a desired feature, the typical user does not want to go to the time and trouble if, even when the visited network provides the feature, the only way to control the feature is to request the assistance of that network's customer service representative. In addition to the problem of dealing with different feature codes used in visited networks, even if the mobile user is not traveling between networks, advances in technology and increased competition between service providers is resulting in the availability of new network features which must be enabled in the mobile stations of existing subscribers within the mobile's home network.
FIG. 1 provides a diagram of the functional entities within a network to illustrate how feature codes are handled in a conventional wireless communications network. Generally, the network consists of the Mobile Station 100, the Base Station 200 and the switching system 300 (designated by dashed lines). Within switching system 300 is the Mobile Switching Center (MSC) 302, for the first network, Home Location Register (HLR) 304 and Visitor Location Register (VLR) 306. MSC 310 is a second Mobile Switching Center corresponding to the home network for Mobile Station 100, which is connected to MSC 302 via conventional wired-based connection for communicating information regarding MS 100 to the visited network. Under current feature code implementation procedures, once MSC 302 receives a "*" or "Menu" input ("Menu" will be seen by the MSC as a star) from MS 100 (via BS 200), it transfers the information to HLR 304, which stores and manages subscriptions, and contains permanent subscriber information. If MS 100 is operating within its home network, HLR 304 will recognize the feature code entered by the mobile user and provide the requested response. If MS 100 is outside of its home network, MSC 302 will transfer information about the mobile station to VLR 304, which contains temporary information needed by MSC 302 to serve visiting mobile stations. If a star key ("*") is pressed followed by two digits to activate a feature code by a visiting mobile station, the message will still be processed through HLR 304. Using procedures established under the IS-41 standard for inter-network communications, MSC 310 is contacted by MSC 302 once it is determined that MS 100 is outside of its home network to provide the information necessary for MSC 302 to communicate with MS 100. Since HLR 304 processes feature codes under current procedures, and since it contains only information regarding the system's own subscribers, it is unable to process feature codes from visiting mobile stations if the requested feature code value differs from its own value. Attempts by a visiting mobile station to access a feature code with a different value, or a feature not supported by the visited system, will be met with a busy signal, or some other indication that the requested feature is unavailable.
Industry efforts are being made to standardize certain feature codes and the requirements for activating them under Telecommunications Industry Association/Electronics Industries Association Interim Standard 52-A (TIA/EIA/IS-52-A), and/or INC 96-0802-015 ("Vertical Service Code Assignment Guidelines"), incorporated herein by reference, which will be of assistance with new networks and new mobile units once the standardization is completed. Delays in implementation of the new standardized feature codes in existing networks are likely to be on the order of two or three years from Final Closure of the issue, which occurred in August 1996.
The newer standards provide for a shift of the processing of feature codes to the Mobile Switching Center, which, while having the advantage of removing the previous limitation created by handling the feature codes in the Home Location Register, still requires standardization of the feature codes amongst all mobile phone manufacturers in order to make sure that every mobile station uses the feature code recognized by the MSCs. Because many mobile phone manufacturers have developed their own systems and preferences, it is unlikely that a consensus could be achieved for adopting a single menu standard or a single numeric sequence for accessing feature codes from every mobile phone, regardless of manufacturer. Further, new features are certain to be added in the future, which will need to be implemented in existing networks and subscriber mobile units. Accordingly, the need remains for means to enable mobile users to readily access network features across multiple networks without requiring the user to learn additional feature codes.